1. FIELD OF THE INVENTION
This invention relates to the field of disk drives, and in particular to a flexible media disk drive that can read and write data onto both low and high density flexible media disks, with two separate interfaces provided for standard and high capacity disks.
2. Background Art
Mass storage for computer or other information systems is typically provided by magnetic media storage systems such as rigid or flexible disk storage systems. A rotating disk having a magnetic media layer on the surface is accessed by a "read/write" head that is used to store and retrieve information from the disk surface. To store information on a magnetic media disk, flux transitions are induced in the magnetic particles embedded in the surface of the disk. When a magnetic read/write head is passed over the flux reversals, a signal is induced in the head that can be decoded to provide information, such as data or position signals.
Typically, data is stored on a magnetic disk in a series of spiral or concentric "tracks" on the surface of the disk. The read/write head moves back and forth radially on the disk so that it can be selectively positioned over one of the tracks. Once in position over a track, the head remains in place as the track rotates circumferentially beneath it, allowing the head to read or write data on the track.
Flexible media disk drive systems, also known as "floppy disk drives" or "floppy drives" are often utilized by computer users to provide random access memory. In a floppy drive, the flexible magnetic media is enclosed in a protective enclosure. An opening in the enclosure is protected by a sliding cover. When the enclosure is inserted into a disk drive, the protective cover slides back, exposing the flexible media to a pair of read/write heads disposed on opposite sides of the disk. Advantages of floppy drives include low cost media and portability. Data security is also an advantage of floppy drives because sensitive material can be written onto a floppy disk, and then removed from the drive as desired. One prior art disadvantage of floppy drives is the limited storage capacity.
Prior art floppy drives typically have been limited to one, two or four megabytes of capacity. As a result, many computer users rely on rigid media disk drives, also known as "hard disk drives" or "Winchester" disk drives, to provide greater storage capacity. Modern disk drives are capable of storing, for example, gigabytes of data, although more popular capacities used in personal computer contexts range from 20 to 360 megabytes. Hard disk drives have fixed media; that is, the media cannot practically be removed from the drive in ordinary use. In addition, rigid media hard disk drives typically are more costly than floppy disk drives.
One scheme to provide a system that combines the portability of floppy disks with the storage capacity of hard disk drives is implemented in the form of a high capacity floppy disk drive as described in U.S. Pat. No. 5,003,412 issued on Mar. 26, 1991 and entitled "Method and Apparatus for Positioning a Read/Write Mechanism" and assigned to the assignee of the present patent application. This patent application is incorporated herein by reference. This patent application describes a novel servo pattern that allows the number of data tracks that can be defined on a flexible media disk to be greatly increased over standard floppy disk drive schemes. This permits implementation of a floppy disk drive that is capable of storing, for example, 25 or more megabytes of data on a single floppy disk.
For purposes of this patent application, a "standard disk drive" refers to a floppy disk drive that can read and write floppy disks with unformatted capacity of one, two or four megabytes of data. A "standard floppy disk" refers to a floppy disk with unformatted capacity of one, two, or four megabytes of data. A "high capacity floppy drive" refers to a floppy disk drive that can read and write floppy disks formatted for 25 or more megabytes of data. A "high capacity floppy disk" refers to a floppy disk formatted for 25 or more megabytes of data.
Both the high density drive and the standard floppy disk drive referred to herein generally use a 31/2" floppy disk form factor, although such drives may use alternate form factors. The floppy disks of the high capacity floppy drive are formatted, however, to store 25 or more megabytes of data as opposed to the one, two, or four megabytes of data of standard floppy disk drives.
Standard floppy disk drives communicate with a host computer system through an interface. This interface is referred to as the "floppy disk interface" and is implemented with a "floppy disk controller." In the prior art, this interface is implemented by inserting an FDC (floppy disk controller) card into a PC-AT bus expansion slot in an IBM or IBM-compatible computer. The FDC card performs the following functions: analog data separator, write precompensation, clock generator, data rate selection and host/drive interface driver/receiver.
A typical high capacity disk drive (example, "winchester" or "hard disk") communicates with a computer system host through a PC/AT bus interface known as the IDE (Integrated Device Electronics) interface. Other industry standard interfaces such as an SCSI (small computer system interface) are commonly used for high capacity disk drive communication as well. The IDE interface is an industry standard interface between computer systems compatible with the IBM model PC/AT computer and many typical hard disk drives. High capacity floppy disk drives can communicate through the IDE interface since their performance and capacity is similar to a hard disk drive.
It is desired to provide a single disk drive that can read from and write to both standard floppy disks and high capacity floppy disks and appear to the host computer as a hard disk with removable media. A computer user who desires to use both types of disks requires separate disk drives compatible with each respective type of floppy disk. This has a number of disadvantages, including the added cost of multiple disk drives, the dedication of expansion capabilities of a .computer system to two devices performing substantially the same function, and the requirement that two different interfaces be implemented.
Therefore, it is an object of the present invention to provide a single disk drive that can read from and write to both standard and high capacity floppy disks.
It is another object of the present invention to provide a disk drive that implements both a floppy disk interface and a IDE interface.
It is another object of the present invention to provide a dual interface disk drive that appears as two different disk drives to a host computer system.
It is another object of the present invention to provide a drive that can be adapted to a standard PC/AT host computer system with no change to the host software or hardware to support the standard floppy.
It is another object of the present invention to provide a means whereby two disimilar interfaces are active concurrently and have access to the same peripheral (floppy disk drive).
It is yet another object of the present invention to provide a means whereby a voice coil motor (actuator) used in a high capacity floppy disk drive can be "transformed" into the equivalant of a stepper motor drive (standard capacity floppy disk drive).